PCBs exist in high concentrations in certain game fish used for human consumption and, as importantly, have been detected in human milk. These facts have raised concern as to the effect that PCBs might have on offspring exposed to these chlorinated hydrocarbons during early post-natal development. In the proposed study we are interested in determining the effect that 3 different doses of PCBs fed to lactating rats during days 1-8 of lactation have on 1) reproductive ability; 2) mating behavior; and 3) activity and learning of the female offspring when they reach adulthood. We are particularly interested in determining if any effects on reproduction, activity and learning are apparent immediately upon reaching maturity or if the effects are delayed. Thus, these parameters will be examined at 3 age-spans--in the young adult, mature adult, and older mature adult rat. The question of interest: is it possible that PCB exposure during a critical time in post-natal development produces adverse effects that become apparent as a premature onset of reproductive aging? The choice of early post-natal exposure to PCBs was made because it is known that development continues in various portions of the CNS post-natally in the rat. Both the hippocampus and cerebellum continue to develop after birth and differentiation of the hypothalamic mechanisms involved in control of gonadotrophin secretion and in reproductive behavior occur neonatally. Thus, an insult to this system from PCBs at this critical time could result in deficits in later reproductive function and in learning and activity. Examination of the effects of PCBs on the latter are of particular interest since these responses serve as indicators of more subtle toxic effects that PCBs may have and which other responses may not reveal. Various responses will be observed in the offspring to determine reproductive ability (e.g., estrous cycling, incidence of implantation, mating behavior). The impact on activity will be determined by observing 6 behaviors (e.g., sniffing, grooming, climbing). The possible effects on learning will be measured using a 14-choice T-maze, since performance on complex tasks has been demonstrated to be sensitive to other forms of CNS insult.